1. Field of the Invention
The present invention is concerned with improvement in or relating to a pneumatic impact imparting tool and more particularly to a pneumatic impact imparting tool which is so constructed that a mechanism for converting rotational movement of a pneumatic motor at a constant rotional speed into intermittent turning movement of an anvil is made integral with the motor.
2. Description of the Prior Art
To facilitate understanding of the present invention a typical conventional pneumatic impact imparting tool as disclosed in U.S. Pat. No. 3,174,597 will first be described with reference to FIGS. 4 to 7. Basically, the conventional pneumatic impact imparting tool is constituted by a combination of a pneumatic motor adapted to be rotated by compressed air, a mechanism for converting rotational movement of the pneumatic motor into intermittent turning movement of an anvil. Incidentally, FIG. 4 is a vertical sectional view of the conventional pneumatic impact imparting tool.
As is apparent from FIG. 4, rotational force transmitting means comprises mainly a pneumatic motor 10 and a hammer 12. Specifically, the pneumatic motor 10 includes a column-shaped rotor 14 having a shaft 13 extended therethrough, a cylinder 16 surrounding the rotor 14, a rear plate 18 secured to the lower side of the cylinder 16 and a front plate 20 secured to the upper side of the same to airtightly close the cylinder 16, as shown in FIG. 5 which is a perspective view of the main components of the pneumatic motor in the disassembled state. To assure that the shaft 13 for the rotor is held rotatably, both the rear plate 18 and the front plate 20 are fitted with bearings 22 and 23. The rotor 14 is formed with a plurality of radially extending grooves 24 in an equally spaced relationship each of the grooves 24 extends from the exterior surface of the rotor 14 inwardly in parallel with the shaft. Further, a vane 26 is inserted in each of the grooves 24 in such a manner that it slides in the radial direction relative to the shaft 13. The shaft 13 of the rotor 14 projects through the front plate 20 and the part of the shaft 13 projected outwardly of the front plate 20 is formed with a plurality of spline teeth 28. Importantly, the inner space of the cylinder is so designed that the center axis of the hollow space is located offset from the center axis of the outer wall of the cylinder 16. Owing to the eccentric construction of the pneumatic motor 10 in that way, the rotor 14 is rotated by means of the vanes 26 as compressed air is introduced into the hollow space between the cylinder 16 and the rotor 14 by utilizing known means.
On the other hand, the hammer 12 includes an anvil 34 adapted to be intermittently turned by rotation of the motor 10 and means for converting rotation of the motor 10 into intermittent turning movement of the anvil 34. Further, the hammer 12 includes a cylinderical cage 36 of which the lower end is closed. The closed end of the cage 36 is formed with a plurality of spline grooves adapted to come in engagement with the spline teeth 28 on the shaft 13 of the rotor 14. Since the cage 36 is made integral with the rotor 14 via spline engagement, it is caused to rotate at the same rotational speed as that of the rotor 14. The anvil 34 is formed with a plurality of spline teeth 38 at its lower end as seen in the drawing. As is best seen in FIG. 7, wings 40 extending in the leftward and rightward directions are made integral with the anvil 34. Both the spline teeth 38 and the wings 40 are accommodated in the interior of the cage 36. A spindle guide 42 against which the lowermost end of the anvil 34 abuts is fixedly secured to the cage 36 so that an annular groove is formed between the outer surface of the spindle guide 42 and the inner wall of the cage 36. A ball 44 is disposed at a predetermined position on the annular groove (at a predetermined position where it turns together with the cage 36).
A cam member 46 as shown in FIGS. 6 and 7 is designed in a cylindrical configuration and a plurality of spline grooves adapted to come in engagement with the spline teeth 38 on the anvil 34 are formed over the cylindrical inner wall of the cam member 46. The cam member 46 is adapted to slide in the axial direction of the anvil 34 while maintaining engagement with the spline teeth 38 of the anvil 34. The lower end part of the cam member 46 constitutes cam face 48 with which the ball 44 is brought in contact. The cam face 48 exhibits a hill-shaped contour as seen from the side. Further, an outwardly projecting annular boss portion 50 is made integral with the cam member 46 around the outer surface thereof. As shown in FIG. 8, the cage 36 is formed with two semicylindrical grooves 53 through which pins 52 are inserted for sliding in the axial direction. Each of the pins 52 is formed with an annular recess 54 which comes into engagement with the annular boss portion 50 of the cam member 46. Accordingly, the pins 52 are caused to slide along the grooves 53 on the cage 36 as the cam member 46 is slidably displaced up and down. Further, a spring 56 is disposed in the hollow space between the surface of the cam member 46 located opposite to the cam face 48 and the wings 40 whereby the cam member 46 is normally urged toward the motor 10 under the effect of the resilient force of the spring 56. A cover 58 is tightly fitted into the opening portion of the cage 36 in order to inhibit the cage 36 and the anvil 34 from being displaced in the transverse direction relative to one another.
Next, description will be made below as to how rotational movement of the rotor 14 at a constant rotational speed is converted into intermittently turning movement of the anvil 34. As the rotor 14 is rotated, the cage 36 is caused to rotate and the ball 44 accommodated at the predetermined position in the cage 36 turns together with the cage 36. When the ball 44 comes in contact with an incline the cam face 48, the cam member 46 is slidably displaced toward the wings 40 by means of the ball 44 against resilient force of the spring 56. As the cam member 46 is slidably displaced in that way, a pair of pins 52 are also slidably displaced toward the wings 40 together with the cam member 46. As a result, the upper part of each of the pins 52 is projected upwardly in the area located by the side of the wing 40. When the cage 36 (pin 52) is rotated further in such a state that the upper parts of the pins 52 are projected upwardly, the pins 52 are brought into abutment against the wings 40, causing the anvil 34 to be turned (see FIG. 7). Thereafter, the ball 44 moves over the hill top of the cam face 48 and thereby the cam member 46 is slidably displaced downwardly to its original position under the effect of resilient force of the spring 56. At the same time the pair of pins 52 are displaced downwardly to the original position where they no longer contact the wings 40.
The cam member 46 does not carry out sliding movement any longer until the ball 44 contacts the inclined part of the cam face 48 after it moves over the hill top of the same. Then, the same operation as mentioned above is repeated when the ball 44 comes in contact with the inclined part of the cam face 48.
As will be apparent from the above description, the motor 10 is made separate from means for converting rotational movement of the motor 10 into intermittent turning movement of the anvil 34. This leads to a drawback that the overall length of the conventional pneumatic impact imparting tool is elongated.